Various processes for the conversion of heavy hydrocarbonaceous fractions, particularly, multi-stage conversion processes include U.S. Pat. No. 4,761,220, Beret et al.; U.S. Pat. No. 4,564,439, Kuehler et al.; U.S. Pat. No. 4,330,393, Rosenthal et al.; U.S. Pat. No. 4,422,922, Rosenthal et al.; U.S. Pat. No. 4,354,920, Rosenthal et al; U.S. Pat. No. 4,391,699, Rosenthal et al.
The present invention relates to a process for the hydroconversion of heavy hydrocarbonaceous fractions of petroleum. In particular, it relates to a close-coupled two-stage; thermal-catalytic, catalytic-hydrotreatment process for petroleum residua having improved effectiveness for high conversion and control of condensation reactions thereby producing stable high-quality products.
Increasingly, petroleum refiners find a need to make use of heavier or poorer quality crude feedstocks in their processing. As that need increases, the need also grows to process the fractions of those poorer feedstocks boiling at elevated temperatures, particularly those temperatures above 1000.degree. F. High conversions to stable, quality products are desirable in order to avoid producing significant quantities of low value fuel oil.
Severe conditions are required in order to achieve high conversions which while producing desirable lighter fractions can also produce thermally cracked fragments and unstable asphaltenes that form mesophase masses. Unless controlled, the cracked fragments can undergo condensation reactions to undesirable polycyclic molecules which tend to be unstable and difficult to process into desirable products. Along with the mesophase masses, they can also lead to coke formation.
It is the intention of the present invention to overcome these problems in a two-stage process which uses coal and a dispersed catalyst in a first stage thermal-catalytic reaction zone which is close-coupled to a second stage catalytic-hydrotreating zone. In the thermal-catalytic zone, the dispersed catalyst catalyses the hydrogenation of thermally cracked fragments and stabilizes them thus preventing condensation reactions. The dispersed catalyst also re-hydrogenates coal liquids which in a non-catalytic process also act to hydrogenate thermally cracked fragments by donating hydrogen to them. The coal liquids also act to solubilize asphaltenes and asphaltenes precursors and inhibit the formation of mesophase masses. The close-coupled catalytic-hydrotreater plays a key role in promptly stabilizing remaining thermally cracking fragments from the first stage, hydrogenating products, removing heteroatoms and effecting some further molecular weight reduction. The unconverted coal and coal ash sequester the metals in the feedstock in the first stage thermal-catalytic zone which results in substantial reduction of metals fouling of the supported hydrotreating catalyst in the catalytic-hydrotreating stage.